This study looks at the recent rise of the public relations profession and its influence on national news production in Britain. Simply put, has public relations undermined the notion of the fourth estate media in Britain and has it advantaged certain kinds of news source over others? The thesis breaks down into three parts. The first part documents the rise of public relations in Britain, its profile, and distribution amongst a range of institutions and organisations. The developing public relations and media industries are compared and the literature, on the relations between 'news sources', PR practitioners and journalists, is critically evaluated. The second part focuses on corporate public relations generally and, more specifically, on financial and City PR. Industry and fieldwork data are contrasted with radical and liberal accounts of media-corporate source relations. The findings suggest that corporate PR has had limited success in influencing mainstream news but been considerably more adept at managing specialist news sections. It is thus argued that PR has benefited the corporate sector, less by influencing journalists and the general public, and more by excluding them. This pattern is supported with a detailed case study involving Granada's take-over of Forte in 1995/96. The third part discusses 'resource-poor' and 'outsider' groups - more specifically, British trade unions. Fieldwork data is used to test radical and pluralist accounts of the coverage of such groups in the mass media. The findings argue that unions have found new ways to increase their media access using PR - and with rather more success than earlier studies suggested. The conclusion is borne out by a case study of the UCW's (Union of Communication Workers) successful PR campaign to halt Post Office privatisation in 1994. Finally, the separate findings of the thesis are used to develop a fuller description of how public relations affects media production and news source access.